I’ve just issued an update to the igneous set of x-eos, involving tiny changes to the thermo of orthopyroxene (provided by Tim Holland). This should prevent high-Ca orthopyroxene from being stable, as has been seen in some calculations on peridotite. I’ll let Jamie Connolly know, so hopefully this change will shortly be implemented in Perple_X too.
Update Oct 2020: This did not solve the problem…. But hopefully the new update to the igneous set, dated 31-10-2020, will do.